878
FXUS63 KUNR 121846
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1246 PM MDT Sat Sep 12 2026

.KEY MESSAGES...

- Cool temperatures for the remainder of the weekend

- Rainfall chances overnight looking a little less likely, with
  better chances coming Sunday night

- Seasonal temperatures through the week, with rainfall chances
  returning by midweek.

&&

.DISCUSSION...(This Evening Through Saturday)
Issued at 1237 PM MDT Sat Sep 12 2026

Latest water vapor imagery shows broad upper high pressure located
across the southern tier of the country with a digging 500hpa low
off of the Pacific NW coast. Quick moving zonal flow is found
across the upper midwest. At the surface high pressure is located
across much of the western Dakotas with a weak surface trough
sliding southeast across eastern SD. At 18Z skies were mainly
clear to partly cloudy except for along the ND/SD border where
more clouds were found. Temperatures were in the mid 50s to mid
60s.

Models are still advertising 700hpa theta-e ridge and associated
forcing to slide across southern tier counties overnight. Did trim
back inherited pops but am still a bit concerned that we might be
overdoing the forecast. Ensembles are only showing 10-20 percent
probabilities of seeing greater than 0.01 inch of rain across our
southern counties, and less than that of seeing 0.05 inch of
rainfall.

Sunday will looks to be dry to begin with and becoming breezy with
easterly upslope flow. This will result in a few more clouds which
will aid in keeping temperatures down a bit more. Sunday night
into Monday morning main upper trough finally kicks out across
region with associated 700hpa theta-e ridge and forcing. Better
moisture tracks along with this feature and this is when our best
chance of seeing rainfall occurs. As the moisture shield tracks
west to east it will become more widespread. Expecting more to
fall is rain, although can`t rule out some scattered
thundershowers here or there through the period.

The remainder of the week looks to be seasonable temperature wise,
with rainfall chances returning back to the forecast area around
mid-week.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Sunday)
Issued At 1245 PM MDT Sat Sep 12 2026

VFR conditions are expected through the TAF period. Gusty
conditions are also expected Sunday afternoon.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&

$$

DISCUSSION...Hintz
AVIATION...Schweigert